1. Field of the Invention
The present invention relates to electronic data storage devices, and more particularly to a data storage device with reduced rotor inertia.
2. Description of Prior Art
Computer disk storage devices include those which utilize one or more rigid magnetic data storage disks directly coupled to the rotor of a spindle drive motor and housed within a “clean room” chamber. Such storage devices typically employ an “outer rotor” brushless DC motor for rotating the storage disks past data read/write heads. The heads write and read digital data on the surface of the disks. In an “outer rotor” brushless motor, a rotor having an annular permanent magnet surrounds a multi-pole stator that is mounted concentrically with the shaft, the shaft defining the axis of rotation of the motor.
FIG. 2 shows a conventional data storage device which comprises a stator 120, a rotor 140, and a plurality of parallel, spaced disks 160 attached to the rotor 140 by a clamp 180. The stator 120 comprises a plurality of radial stator laminations 122. A winding 124 is wound around each stator lamination 122. The rotor 140 comprises a shaft 142 rotatably attached to the stator 120 by a pair of bearings 144, and a hub 146 fixed around the shaft 142. A magnet 148 is attached to a radially extending portion 147 of the hub 146, and opposes free ends of the stator laminations 122. When the windings 124 are electrified, the magnet 148 drives the combined rotor 140, disks 160 and clamp 180 to rotate about the shaft 142.
However, the outer rotor data storage device employs the rotor 140 that encompasses the stator element. The rotor 140 therefore requires a diameter that adds to the mass and angular inertia of the rotor 140. This increases the time required for a motor of the data storage device to reach a desired operating speed at startup. The radially displaced mass also amplifies vibration due to imbalances, especially at higher operational speeds. Furthermore, the shaft 142 is essentially a cantilever structure, with only one end of the shaft 142 being fixed with the hub 146. This also amplifies vibration and instability.